As combines have increased in size and weight over the years, considerable structure has been added to the rear axle to support the added loading. Conventionally, combines have utilized a rear axle that has a central, fore-and-aft pivot so the axle can tilt from side-to-side relative to the chassis as changes in ground contour are encountered. In large combines, such a center pivot requires the presence of massive support structure from side frames of the chassis to the center pivot, plus a reinforced axle beam to return the loading out to the ground wheels at opposite ends of the axle. Thus, providing a center pivot rear axle on large, heavy combines gives rise to a number of significant issues.
The present invention provides a combine harvester that achieves the desired center pivot capability for the rear axle without the attendant massive support structure heretofore required in conventional machines. In this regard, the present invention provides a rear axle that is suspended from the chassis such that it not only affords the desired center pivot ability without massive support structure, but also provides reduced shock loading on the chassis, the ability to adjust the fore-and-aft attitude of the combine either manually or automatically, and the ability to achieve enhanced steering of the rear wheels. In a preferred form of the invention, the rear axle of the combine comprises a suspension axle assembly that includes a transverse axle swingably mounted to the chassis for up-and-down movement relative thereto. Suspension apparatus in the form of expandable resilient devices, hydraulically or pneumatically operated, is disposed between the axle and side frames of the chassis to cushion the load and to provide a means for transferring such load to the axle adjacent the ground wheels. The expandable devices can be expanded independently of one another to permit tilting of the axle from side-to-side, or they can be expanded in unison for controlling the fore-and-aft attitude of the machine. In one embodiment of the invention, the suspended axle can be shifted to a certain extent longitudinally, i.e., side-to-side of the combine, to enhance steering.